What s wrong with the polygons of my model
What has happened is the normals on you faces have flipped.  This will sometimes happen when you scale a mesh negatively or you extrude a face in a negative direction local to the face.  One way to see these faces is by disabling backface culling.  But I would not recommend this, because all it does is makes both sides of the faces visible in the viewport.  When you render you will still get dark looking faces.  For a permanent fix, go into Edit Mode, press A to select all faces.  Then select recalculate normals under Shading/UVs in the tool bar, or just press CTRL+N